In the oak bark contains 10-20% of tannins, free gallic and ellagic acids, catechins, flavonoids, triterpenoids, sitosterol, vitamins B1, AT2, AT6, pantothenic, ascorbic acids, macro- and microelements and other biologically active substances.
Decoction of the bark of oak has astringent, anti-inflammatory effect, due to the presence of tannins.